Very low speed performance of active flux based sensorless control: interior permanent magnet synchronous motor vector control versus direct torque and flux control

This study is focused on very low speed performance comparison between two sensorless control systems based on the novel 'active flux' concept, that is, the current/voltage vector control versus direct torque and flux control (DTFC) for interior permanent magnet synchronous motor (IPMSM) drives with space vector modulation (SVM), without signal injection. The active flux, defined as the flux that multiplies iq current in the dq-model torque expression of all ac machines, is easily obtained from the stator-flux vector and has the rotor position orientation. Therefore notable simplification in the rotor position and speed estimation is obtained. For IPMSM, a stator-flux observer is employed based on combined current and voltage models, with speed-dependent smooth transition between them using a PI compensator of flux error. Comparative experimental results using both sensorless control systems are presented to verify the principles and to demonstrate the effectiveness of the active flux observer at very low speeds from 20 to 2 rpm (1–0.1 Hz).